WO2002062904A1

WO2002062904A1 - Thickened aqueous coating compositions containing film-forming polymeric binder

Info

Publication number: WO2002062904A1
Application number: PCT/EP2002/000516
Authority: WO
Inventors: Manish Sarkar; Stephane Patrick Belmudes
Original assignee: Imperial Chemical Industries Plc
Priority date: 2001-02-07
Filing date: 2002-01-16
Publication date: 2002-08-15
Also published as: CN1491263A; MXPA03007065A; CN1232594C; US20030004261A1; US20020151643A1; PT1368438E; GB0102943D0; EP1368438A1; EP1368438B1; AR032254A1; ATE323137T1; MY127725A; BR0206962A; BR0206962B1; ES2261640T3; US6740703B2; DE60210589D1; US6903157B2; DE60210589T2

Abstract

A thickened aqueous coating composition (preferably paints and the like or adhesives) containing a film-forming polymeric binder which produces dried coatings having less sensitivity to water by using a thickener which is autoxidisable. Preferred autoxidisable moieties are provided by long chain fatty acids of the type used in alkyd paints and association is the preferred thickener mechanism. The moieties may form part of a compound which can take part in a copolymerisation to form a cellulose-free polymeric backbone for the thickener and if the compound is not very soluble in water, the copolymerisation mixture is subjected to intensive agitation to form droplets of less than 500nm number average diameter which compensates for the lack of solubility. The thickener may serve as a binder if sufficient amounts are used.

Description

THICKENED AQUEOUS COATING COMPOSITIONS CONTAINING

FILM-FORMING POLYMERIC BINDER

This invention relates to a thickened aqueous coating composition

containing film-forming polymeric binder and a macromolecular thickener. It also

relates to a macromolecular thickener for use in the composition and to a

polymerisable compound for use in making the thickener.

Thickened aqueous coating compositions are commonly used in coating

surfaces found in buildings where the surfaces are usually coated at ambient

temperatures of say 5 to 40°C using for example brushes, rollers, pads or sprays as

the application tools. Such compositions are often called "architectural" coating

compositions and they include paints, lacquers, varnishes, woodstains and adhesives. Thickening a coating composition facilitates its loading onto

application tools and its subsequent application onto architectural surfaces.

A thickened aqueous coating composition usually contains not only

macromolecular thickener, water and a polymeric binder, but also particulate non-

binder solids such as inorganic and/or organic pigments or opacifiers (for example

rutile titanium dioxide or polymeric organic particles containing voids) or

extenders (for example chalk, dolomite, clays or talc) as well as other optional

ingredients such as matting agents (for example silica), structuring agents (for

example titanium or zirconium chelates or laponite or bentonite clays), coalescing

solvents (for example moderately volatile alcohols such as benzyl alcohol or

hydrocarbons such as white spirit), antifoaming agents and biocides. After a

thickened aqueous coating composition has been applied to a surface, it will dry

and lose water whereupon the binder forms a film which binds together the

remaining ingredients of the composition and the film bonds to the surface to form

a dried coat on the surface.

A problem with dried coats obtained from thickened compositions is that

residual thickener in the coat introduces a degree of water-sensitivity which

manifests as a reduced so-called "wet wipe-resistance" together with a tendency

for the dried coat to soften when wet which problem will be called "wet-

softening". For this reason, thickener concentrations are usually kept below 2wt%

of non vol thickener per lOOg paint composition. The problem is especially

troublesome if the dried coat has been obtained from a fluid coating composition

in which the volume of particulate solid material is below 30 vol% (based on the total volume of the fluid coating composition) and especially when the volume of

the binder in the composition is below 20 vol%. This is because amounts of

thickener well above 3wt% are needed to give the coating compositions

viscosities which are high enough for practical use. The problem is further

aggravated if the dried coat contains a high volume percentage of particulate non-

binder solids for such dried coats are less strongly bound and so are more

sensitive to water. The volume percentage of non-binder particulate solids in a

dried coat is conventionally called "Pigment Volume Content" or "PNC" even

though solids other than pigments may be involved. Serious water-sensitivity

arises in conventional dried coats if the PNC is above 70%.

Thickeners inevitably introduce further water-sensitivity into a dried coat

because they are necessarily hydrophilic materials as will be explained towards

the end of the following brief review of their usefulness in architectural coating

compositions. A good account of thickeners and the closely related materials often

known as "rheology modifiers" is given by G D Shay in Chapter 30 (headed

"Thickeners and Rheology Modifiers") of the book "Paint and Coating Manual:

14^th Edition of the Gardner-Sword Handbook" edited by J N Koleske and

published in 1995 by ASTM of Philadelphia. The contents of this Chapter 30 are

herein incorporated by reference. The distinction between "thickeners" and

"rheology modifiers" is somewhat arbitrary and so for the purposes of this

Specification, the term "thickener" will be used to include "rheology modifier"

too. Shay describes "rheology modifiers" as "inefficient thickeners" which have to be used in concentrations of over 18g/litre (i.e. over 1.8wt%) if a useful

thickening effect is needed.

Shay explains that architectural coating compositions need to have

viscosities which are high enough under all rates of shear, namely under high

shear rates of over 1000/sec, moderate shear rates of from 10 to 1000/sec and low

shear rates of below 10/sec. In the field of architectural coatings, viscosity is

conveniently measured at 18°C using a concentration of 2wt% thickener based on

the combined weight of water and thickener. A suitable high shear rate viscosity

enables the coating compositions to be applied by brush, roller or pad in

thicknesses which allow the resulting dried coat to hide blemishes on a surface

and so minimise the need for further coatings to be applied. Preferably the high

shear rate viscosity should be from 0.05 to 0.25 Pa.sec when measured by an ICI

Cone and Plate viscometer as described in ASTM Test D 4287-88, the contents of

which are herein incorporated by reference.

A suitable moderate shear rate viscosity facilitates mixing and pumping

operations during the manufacture of the coating composition and also gives them

a so-called "consistency" which appeals subjectively to many users. Preferably

the moderate shear rate viscosity should be from 0.1 to 2.0 Pa.sec when measured

by a Sheen Rotothinner viscometer as described in the Sheen Data Sheet called

"Sheen/ICI Rotothinners" available from Sheen Instruments Ltd of Kingston on

Thames, England. The contents of this Data Sheet are herein incorporated by

reference. A suitable low shear rate viscosity inhibits settling of solid ingredients

when the coating compositions are being stored. Secondly, such a low shear rate

viscosity reduces the risk of liquid coating compositions flowing down vertical

surfaces to which they have just been applied. Such flow creates a disfiguration

known as "sagging". Thirdly, it enables large amounts of coating composition to

be loaded onto a tool such as a brush or roller. Preferably the low shear rate

viscosity should be from 20 to 150 Pa.sec when measured by a Brookfield

viscometer as described in ASTM Test D2196 using Spindle No. 3 at a rotation

speed of 12 rpm. The contents of ASTM Test D2196 are herein incorporated by

reference.

Most formulations of film-forming polymeric binders and particulate solids

in water do not have a sufficiently high viscosity under one or more of the shear

rate conditions discussed above. This is particularly true if the fluid coating

composition contains less than 30 % by volume of solid materials and especially if

it contains less than 20 % of binder.Therefore, as reported by Shay, the viscosities

of the formulations are conventionally increased by the addition of from 3 to 18g

of a thickener per litre of coating composition,ie concentrations of 0.3 to 1.8wt%.

According to Shay, the increase in viscosity is caused by broadly one of three

mechanisms operating either alone or in combination. The three mechanisms are

known as "hydrodynamic", "flocculative" and "associative". All three comprise

interactions which involve macromolecules containing polymeric backbones

having high weight average molecular weights of over 30,000 and preferably over

50,000. Viscosities at all three shear rates can be conveniently measured together

using a "Carri-Med" CSL 100 rheometer as supplied by TA Instruments Limited

of Leatherhead, England.

The hydrodynamic mechanism is the primary mechanism employed by

traditional macromolecular thickeners such as the gums, cellulose derivatives,

polyethoxylates, polyacrylamides, polyvinyl alcohols and others listed by Shay in

his Table 2. The mechanism requires a water-sensitive macromolecular thickener

comprising a high molecular weight hydrophilic backbone devoid of any

significant hydrophobic character. On adding the thickener to water, its

hydrophilic backbones uncoil and occupy a large hydrodynamic volume in the

solution so immobilising large volumes of water and thereby creating a substantial

increase in viscosity.

The flocculative mechanism is a mechanism also employed by traditional

thickeners comprising high molecular weight hydrophilic backbones which are

water-sensitive and devoid of significant hydrophobic character. In this

mechanism, the hydrophilic nature of the thickener causes it to concentrate with

the water into predominantly aqueous regions of the coating composition whilst

particles of polymeric binder form and concentrate in predominantly hydrophobic

regions. The concentrated binder particles touch each other and form floes which

impede flow and thereby substantially increase the viscosity of the coating

composition.

The associative mechanism requires a more recent type of thickener known

as an "associative thickener" such as those listed by Shay in his Tables 4 and 5. Like traditional thickeners, associative thickeners are macromolecular and must

raise the viscosity of water or other aqueous media either by virtue of their

solubility or because they become water soluble by a simple change in pH, for

example by the neutralisation of acidic or basic groups incorporated into the

thickener. They must also contain a high molecular weight backbone having

hydrophilic character. However, in associative thickeners, the hydrophilic

moieties are adjacent to hydrophobic moieties sometimes called "hydrophobic

modifications". When the associative thickener is added to an aqueous coating

composition, the hydrophilic moieties attract large volumes of water whilst the

hydrophobic moieties associate with like moieties on other backbone chains

and/or they associate with hydrophobic moieties on hydrophobic particles in the

composition such as particles of binder or pigment, opacifier or extender. This

association creates shear reversible three-dimensional physical networks which

are bulky and entrap large volumes of water thereby impeding flow and causing a

substantial increase in the viscosity of the coating composition.

It will be seen from the above review that the presence of hydrophilic

character is essential to the mechanism by which thickeners thicken aqueous

coating compositions. This means that the presence of hydrophilic residues is

inevitable in dried coats obtained from thickened coating compositions which

explains why the use of thickeners has hitherto been inevitably linked with an

increase in the water-sensitivity of the dried coats. An illustration of the use of a

particular type of thickener in an aqueous coating is provided by Partan in US

5,504,123 issued in 1996. Partan discloses the use of an associative thickener comprising high molecular weight (10,000 to 500,000) water-sensitive cellulose

ether chains onto which have been grafted autoxidisable moieties (as described

later in this specification) containing from 4 to 20 carbon atoms. When a coating

of the composition is allowed to dry, the moieties autoxidise and produce a dried

coat which is harder and more durable. A problem with cellulose ether chains is

that their hydroxyl groups cause high viscosities in water and unfortunately, the

grafting of the autoxidisable moieties onto cellulose ether chains which already

have a high viscosity produces even higher viscosity thickeners which accordingly

can only be used in low concentrations in the coating compositions, for example

concentrations of 0.05 to 3 wt % as proposed by Partan. Reducing the molecular

weight of such cellulose ether chains in order to reduce the viscosity increases the

water sensitivity resulting in poorer performance. The inability to use high

concentration of autoxidisable cellulose ether thickeners is an especial

disadvantage when the dried coats have been obtained from fluid coating

compositions containing less than 30 vol% of particulate solids and more so if the

dried coats also contain less than 20 vol% of binder and that this is particularly so

if the dried coat has a high PVC, for example a PVC of above 70%.

An object of this invention is to provide thickened aqueous coating

compositions containing a macromolecular thickener and a film-forming

polymeric binder which compositions produce dried coats of less water-sensitivity

and so can tolerate larger concentrations of thickener. Another object is to

provide thickened coating compositions containing low volumes of solid

materials, especially binder which can nevertheless give dried coats having a PVC of over 70% and which have adequate resistances to wet-wiping and wet-

softening. A related object is to provide a thickener for use in such coating

compositions and a polymerisable compound for use in making the thickener. A

further object it to provide a thickener which can in some circumstances also serve

as the polymeric binder so avoiding the need for the coating composition to

contain a separate polymeric binder.

Accordingly, this invention provides a thickened aqueous coating

composition of a chosen pH which contains a polymeric binder and a

macromolecular thickener

a) which thickener contains macromolecules having moieties which are

hydrophilic at the chosen pH and

b) which thickener on dispersion in water at a concentration of 2wt%

(based on the combined weights of the thickener and water) has a

low shear viscosity of at least 0.1 Pa.sec (preferably 1 to 20 Pa.sec)

when measured at 18°C on a Brookfield viscometer using a No. 3

Spindle rotating at 12rpm

wherein the macromolecules are cellulose-free and contain autoxidisable moieties

thereby creating a cellulose-free autoxidisable thickener. The compositions may

contain over 3wt% (often even over 10wt%) of thickener and still be easy to

handle and give dried coatings which are not unduly water-sensitive. Of course

compositions containing less than 3wt% of the thickener may also be made. The

coating compositions are preferably architectural coatings including paints,

lacquers, varnishes, woodstains and adhesives. "Autoxidisable moieties" are moieties which can react with oxygen at

ambient temperatures usually in the presence of catalyst known as a "drier" to

produce crosslinks to other oxidisable moieties on adjacent like macromolecules.

Autoxidation is the process by which conventional solvent borne alkyd paints

form dried coats having amongst other things good wet-wipe and wet-softening

resistences. It has now been found that autoxidation can likewise confer wet-wipe

and wet-softening resistances on dried coats obtained according to this invention

including those having a PVC of over 70% and/or obtained from fluid coating

compositions containing only low volumes of solid particulate materials. A good

account of the way in which alkyd paints oxidise is given on pages 156 to 160 of

the book "Introduction to Paint Chemistry" by GPA Turner published in 1988 by

Chapman and Hall of London. The contents of these pages are herein

incorporated by reference. It should be explained that this type of oxidation is

also known as "drying" even though the oxidation mechanism itself does not

depend on the loss of liquid by volatilisation. Turner illustrates autoxidisable

moieties which comprise ethylenic double bonds and "driers" which are soaps of

polyvalent metals such as for example the octoates or naphthenates of cobalt or

manganese and which catalyse the autoxidation reaction. Zirconium soaps are also

used as driers. Driers are used in various concentrations and these can be readily

determined by those skilled in the art. Typically, up to 0.2wt% of the metal based

on the total paint composition is used.

Autoxidation may be accelerated by the presence of easily oxidised

compounds and especially polyunsaturated compounds such as maleinised polybutadiene where the polybutadiene moieties have a weight average molecular

weight of from 3,000 to 7,000 and where the maleic moieties provide

dispersibility in water. Preferably the coating composition contains from 0.1 to

lwt% of these easily oxidised compounds.

Autoxidisable moieties may be obtained from a wide variety of unsaturated

materials, but those most commonly used in, for example, alkyd paints are derived

from long chain unsaturated fatty acids containing from 12 to 30 carbon atoms. A

list of such fatty acids is provided on pages 215 and 216 of Volume 1 of the book

"Outlines of Paint Technology" by W M Morgans and published in 1982 by

Griffin of London and the contents of these pages are herein incorprated by

reference. Amongst the commercially more important fatty acids listed by

Morgans are linseed oil fatty acid, soya bean oil fatty acid, safflower and

sunflower oil fatty acids and tall oil fatty acid. These long chain fatty acids are

also examples of fatty acids useful in making the autoxidiseable thickeners of this

invention. Use of such long chain fatty acids also has the advantage of

introducing hydrophobic moieties into the thickener providing it with means for

use in associative thickening mechanisms.

A most preferred technique for introducing the autoxidisable moieties

involves taking a copolymerisable compound, or monomer, containing a long

chain unsaturated fatty acid moiety and copolymerising it with other monomers

used in the production of the thickener macromolecules. Some of these other

monomers will have moieties which are hydrophilic at the pH chosen for the

coating composition. In effect, the copolymerisation creates a macromolecule having a backbone which contains hydrophilic moieties adjacent to hydrophobic

long chain fatty acid moieties which depend from the backbone. A reaction

scheme for this type of copolymerisation is shown in Figure 1 of the drawings.

Preferably, the copolymerisable compound containing the fatty acid moiety should

comprise from 2 to 30wt% (and especially 4 to 15wt%) of the monomers which

are copolymerised to create the macromolecules of the thickener. Generally the

monomers containing the hydrophilic moieties should comprise from 10 to 40

wt% (especially from 20 to 40 %) of the monomers copolymerised to create the

macromolecules.

Conveniently available co-monomers for use in forming the remainder of

the polymeric backbone include alkyl esters of unsaturated carboxylic acids such

as the methyl, ethyl, butyl and 2-ethylhexyl esters of acrylic or methacrylic acids,

vinyl esters such as vinyl acetate or vinyl "Versatates"¹, α-olefins such as

ethylene, propylene or butene-1 and styrene or its homologues. Copolymerised

styrene and its homologues have the additional advantage of being particularly

active in generating and coupling to free radicals and so they promote the

autoxidation process which in turn accelerates the onset of water-resistance.

The hydrophilic character which is essential to the thickening mechanisms

may be provided by co-monomers containing hydrophilic moieties such as

hydroxyl or ionic groups. Examples of co-monomers which can provide hydroxyl

groups include hydroxyethyl acrylate or vinyl acetate after it has been

¹ Vinyl "Versatate" is the vinyl ester of so-called "Versatic" acid which is a mixture of aliphatic monocarboxylic acids each containing an average of 9, 10 or 11 carbon atoms and is commercially available from the Shell Chemical Company of Carrington, England. subsequently hydrolysed to give a notional copolymerised vinyl alcohol. Other

co-monomers such as carboxylic acids or their anhydrides or amides can introduce

hydrophilic character provided that an appropriate pH is chosen for the coating

composition. Choosing a pH above 7 converts carboxylic groups in the

copolymerised carboxylic acids or anhydrides into hydrophilic carboxylate anions.

Again, suitable carboxylic acid/anhydrides include acrylic, methacrylic, crotonic

or itaconic acids or maleic or succinic anhydrides. Likewise choosing a pH below

7 converts amino and amido groups in copolymerised amino/amides to

hydrophilic cations. Suitable amino/amide co-monomers include

dimethylaminoethyl or tertiarybutylaminoethyl methacrylates or acrylamide or

methacrylamide. Sodium acrylamidopropane sulphonic acid is an example of a

co-monomer which can be given either an anionic or a cationic hydrophilic

character.

The copolymerisable compound containing the fatty acid moiety may be

the diester formed by reacting the long chain fatty acid with the oxirane group in

an ethylenically unsaturated monomer such as glycidyl acrylate or methacrylate.

Such a reaction produces a copolymerisable autoxidisable monomer of

hydroxypropylene diester comprising unsaturated long chain fatty acid moiety

linked to an unsaturated carboxylic acid ester by the divalent hydroxypropylene

group. The unsaturation in the unsaturated carboxylic acid ester is then available

for copolymerisation with the other monomers to form the backbone of a

thickener macromolecule whilst the unsaturation in the dependant long chain fatty

acid derivatives renders the thickener autoxidisable. Preferably the copolymerisable compound is stored at low temperature to improve its storage

stability.

Hydroxypropylene diesters being the reaction products of unsaturated long

chain fatty acids and copolymerisable carboxylates have the advantage of being

relatively easily available but they also suffer the disadvantage of having a very

low solubility in water which inhibits their activity in conventional aqueous

copolymerisation processes unless environmentally unwelcome amounts of

organic co-solvent are also present. It has been discovered that this problem can

be solved by stirring the co-monomers (including the copolymerisable compound

such as the diester) together with water, polymerisation initiator and surfactant

and then subjecting the stirred mixture to intensive agitation sufficient to create a

very large number of very small (less than 500nm in diameter) droplets of co-

monomer. The polymerisation initiator may be water soluble or oil soluble; that is

to say soluble in the monomers. When an oil soluble initiator, such as lauroyl

peroxide is used, it is preferred that it is first dissolved in the monomers and

subjected to the intensive agitation prior to causing the polymerisation to proceed.

When a water soluble polymerisation initiator is used, such as for example

ammonium persulphate, it may be added either before or after intensive agitation.

When such a water soluble initiator is used, copolymerisation is initiated in the

water phase but then the copolymerising system will migrate into organic zones

created by the droplets where copolymerisation will continue. The migration will

be quick because it is favoured by the high surface area provided by the very large

number of very small droplets of co-monomer. This migration permits effective copolymerisation of very low water-solubility monomers, in this case the

autoxidiseable copolymeriseable compounds.

The most preferred diester comprises methacrylate moieties and moieties

derived from tall oil fatty acid.

Polymerisation can be effected by raising the temperature. Preferably

temperatures of 30 to 98^°C are used. Additionally and alternatively, a redox

initiator system may be used. Suitable examples of such systems include hydrogen

peroxide and ascorbic acid, ammonium persulphate and sodium metabisulphite or

sodium sulphoxylate formaldehyde. Optionally, metal salts such as copper or iron

salts may be added.

The required intensive agitation may be provided by mechanical

emulsifiers such as a Ross 100 (available from Ross and Son, Hauppauge, New

York, USA) or a Silverson (available from Silverson Machines Ltd, Chesham,

Buckinghamshire, UK) or an IKA emulsifier (available from IKA- Works Inc,

Cincinnati, Ohio, USA). Alternatively, a Sonolator (available from Sonic Corp,

Stratford, Connecticut, USA) may be used which employs ultrasound to generate

the required shear. Preferably, agitation is sufficiently energetic to produce

eventual particles of thickener which in the unneutralised state have a number

average particle size of below 500nm and preferably below 300nm.

A more hydrophilic diester would have the twin advantages of being

capable of a purely aqueous emulsion copolymerisation without the need for

intensive agitation and greater efficiency as a thickener. One way to increase

water solublity of the water-insoluble diesters is to introduce hydrophilic character into otherwise hydrophobic groups pendant from the polymeric backbone. This

can be conveniently done by linking the fatty acid derivatives to the unsaturated

carboxylate by means of a polyethoxylate or similar polyether divalent radical

instead of by the divalent hydroxypropylene group used above.

Alternative techniques for obtaining useful copolymerisable diesters

involve alcoholysis followed by an esterification or transesterification. Preferred

techniques comprise the alcoholysis of an unsaturated triglyceride by a polyol

which is usually a diol. The alcoholysis converts the triglyceride to a mixture

containing mono- or di-glycerides which contain respectively two or one

hydroxyls whilst at least some of the polyol is converted to an ester containing at

least one hydroxyl. These hydroxyls provide means for bonding the esters to

monomers copolymerisable with the other co-monomers which copolymerise to

produce the thickener macromolecule. Preferred triglycerides are the oils used as a

source of the unsaturated long chain fatty acids mentioned above, especially

linseed oil, soya bean oil, safflower seed oil, sunflower seed oil or tall oil.

Preferred diols are 1,3 butene diol and neopentyl glycol.

The above hydroxyl containing esters may be bonded to copolymerisable

monomers to form a diester by co-reaction with carboxylic acid groups,

carboxylic anhydrides or oxirane groups associated with the monomer or by a

transesterification. The preferred co-reactants are anhydrides and particularly

methacrylic anhydride. Transesterification is preferably performed using Ci _{t0 8}

alkyl esters of unsaturated carboxylic acids such as the methyl, ethyl, butyl, or

ethoxyhexyl esters of acrylic, methacrylic, crotonic or itaconic acids. Both the co- reaction and the transesterification each produce unsaturated diesters useful in

making thickener macromolecules. However, the intense agitation technique may

need to be employed if the diesters are not very water-soluble.

In the field of thickener macromolecules, the polymeric backbone of the

macromolecule is generally regarded as being the longest chain of carbon atoms

optionally also containing oxygen and/or nitrogen atoms which exists in the

macromolecule excluding any primary hydrophobic side chains. Examples of

typical polymeric backbones are shown in Figures 2 to 4 of the drawings. Other

moieties such as hydrophobic, hydrophilic and especially the autoxidisable

moieties may depend from the backbone. The backbone should have a molecular

weight average of at least 35,000, preferably at least 50,000 and usually from 10⁵

to 10⁶.

In addition to increasing the viscosity of the coating composition and

decreasing the water-sensitivity of the dried coats, the thickener may also

autoxidise to form a binder film and so if sufficient autoxidisable moieties are

present, the thickener may serve as the sole binder. The amount of

autoxidisability needed will depend on the PVC of the composition with higher

PVC's needing more autoxidisability especially where the PVC exceeds 70%.

This invention also provides an aqueous thickener dispersion of chosen pH

for use in coating compositions

a) which thickener contains macromolecules having moieties which are

hydrophilic at the chosen pH and b) which thickener on dispersion in water at a concentration of 2wt%

(based on the combined weights of the thickener and water) has a low

shear viscosity of at least 0.1 Pa.sec when measured at 18°C on a

Brookfield viscometer using a No. 3 Spindle rotating at 12rpm

wherein the macromolecules are cellulose-free and also contain autoxidisable

moieties, thereby creating a cellulose-free autoxidisable thickener.

This invention further provides an autoxidisable copolymerisable

compound for use in making a thickener according to this invention wherein the

compound is a diester containing a divalent hydroxypropylene group or a divalent

polyoxyethylene group and moieties which are esters of acrylic and/or methacrylic

acid and a long chain unsaturated fatty acid moiety.

Procedure for Assessing Wet-Wipe Resistance:

The Wet- Wipe Resistance of a dried coat of paint is assessed as follows:

The surface of a board is painted with a commercial vinyl acrylic high PVC

emulsion paint (Dulux® Supermatt) by spray application at a spreading rate of

approximately 10 square metres per litre and allowed to dry at room temperature

(15 to 20°C) for 48 hours. The painted surface is then further painted with a brush

using the thickened aqueous paint which is to be assessed. The newly painted

surface is allowed to dry at room temperatures for one hour and then different

samples of the painted surface are stored at room temperatures for periods of one,

two, three and four weeks respectively. After storage, each sample is wiped 20 times with a wet rag and the amount

of paint removed is assessed visually and assigned a value according to the

following scale:

1 = very poor, paint removed within 1 - 5 wipes. 3 = quite poor, giving soapy sensation at 10 wipes, lots of paint on rag.

5 = poor, giving soapy sensation at 18 - 20 wipes.

7 = little paint removed, gives no soapy sensation.

10 = no paint removed at all.

The invention is further illustrated by the following Examples of which

Examples A to C are comparative.

EXAMPLE 1

Process for the Production of a Copolymerisable Cellulose-free Autoxidisable

Monomer:

500g of tall oil fatty acid (TOFA), 8.0g of cetyl trimethyl ammonium

bromide and 0.7g of hydroquinone were all charged under nitrogen to a one litre

round bottom flask fitted with a reflux condenser and a stirrer. The contents of the

flask were stirred and heated to 80°C and then 355.0g of glycidyl methacrylate

were added gradually over a period of 3 hours whilst a temperature of 80°C and

stirring were maintained. The temperature of 80°C and the stirring were

maintained for a further 9 hours.

During the process, TOFA reacted with oxirane moieties in the glycidyl

methacrylate to form a copolymerisable diester in which unsaturated methacrylate

moieties were linked to an autoxidisable TOFA carboxylate by a

hydroxypropylene divalent group. The reaction was catalysed by the cetyl trimethyl ammonium bromide and premature polymerisation was inhibited by the

hydroquinone. The resulting monomer was stored in a fridge at about 4°C prior to

use. A molar excess of the glycidyl methacrylate over TOFA is used.

EXAMPLE 2

Alternative Process to that of Example 1:

The procedure of Example 1 was repeated except that the catalyst was

11.3g of tetra-ethyl ammonium bromide, the addition of the glycidyl methacrylate

was made over a period of two hours and the temperature of 80°C and stirring

were maintained for a further 3 hours instead of 9.

As in Example 1, the reaction of TOFA and glycidyl methacrylate formed a

copolymerisable diester. . The resulting monomer was stored in a fridge at about

4°C prior to use.

EXAMPLE 3

Alternative Copolymerisable Cellulose-free Autoxidisable Monomer having a

Greater Hydrophilicity:

40.0g of a hydroxypolyethoxy tall oil carboxylate (in this case Tall oil fatty

acid ethoxylate with 6 ethylene oxide units) and 0.2g of hydroquinone were

charged under nitrogen to a one litre round bottom flask fitted with a reflux

condenser and a stirrer. The polyethoxy moiety contained a number average of 6

ethoxy units. The contents of the flask were stirred and heated to 100°C and then

15.0g of methacrylic anhydride were added over a period of one hour. The

temperature of 100°C and the stirring were maintained for a further 3 hours. During the process, the hydroxypolyethoxy moiety esterified the

methacrylic anhydride to form a copolymerisable diester in which unsaturated

methacrylate moieties became linked to tall oil carboxylate by a polyethoxy

divalent group. The presence of the polyethoxy link conferred increased

hydrophilicity on the diester as compared with the hydrophilicity of the

autoxidisable monomer produced in Examples 1 or 2.

EXAMPLE 4

Process for the Production of an Autoxidisable Cellulose-free Thickener

which will be called "Thickener Eg 4":

The following co-monomers and hexanol were mixed together in a glass

beaker at ambient temperatures:

Ethyl Acrylate 165.00g

Methacrylic Acid 94.00g Methyl Methacrylate 5.60g

Copolymerisable Monomer of Example 1 23.50g

Hexanol 1.35g

The mixture was added slowly with stirring to a solution of 2.00g of

sodium dioctyl sulphosuccinate (SDSS) surfactant in 386.00g of water. The new

mixture so obtained was subjected to intensive agitation for 10 minutes using a

Silverson mixer rotating at high speed whereupon an emulsion was obtained

comprising very fine droplets of organic monomers.

The emulsion was gradually pumped over 3 hours into a solution of 0.10g

SDSS surfactant and 2.50g ammonium persulphate polymerisation initiator

in 808.20g water maintained at 80°C under nitrogen in a round bottom flask fitted

with a reflux condenser and a stirrer. Copolymerisation began and the

temperature of 80°C and stirring were maintained for a further 30 minutes after

pumping had been completed. Then a second solution comprising 0.27g of

5 ammonium persulphate in 2.20g water was added followed by a second period of

30 minutes at 80°C with stirring. Lastly, a solution of 0.18g sodium sulphoxylate

formaldehyde 2.00g water was added followed by a final period of 30 minutes at

80°C with stirring. The contents of the flask were filtered and a latex of

particulate macromolecular thickener was obtained in which the particles had a

l o number average particle size of 314nm.

The macromolecules contained a backbone consisting of copolymerised

acrylate, methacrylate and methacrylic acid moieties which acid moieties confer

hydrophilic character on the macromolecules when they experience a change in

pH to above 7. Hydrophobic moieties comprising tall oil carboxylate depend

15 from the backbone to which they are connected via a divalent hydroxpropylene

group. The hydrophilic moieties and their adjacent hydrophobic moieties allow

the macromolecules to act as an associative thickener when in solutions of pH

above 7 and preferably between 9 to 9.5.

EXAMPLE 5

20 Autoxidisable Cellulose-free Associative Thickener containing Styrene as

Autoxidation Promoter which will be called "Thickener Eg 5":

The process of Example 4 was repeated but with the following

modifications: 1. The mixture of co-monomers was as follows:

Ethyl Acrylate 165.00g

Methacrylic Acid 92.00g

Methyl Methacrylate 6.20g Styrene 15.00g

Copolymerisable Monomer of Example 1 26.00g

2. The surfactant solution contained 5.00g of SDSS in 386.70g of water.

3. The initiator solution in the round bottom flask consisted of 0.1 Og of SDSS and 2.50g of ammonium persulphate in 808.00g of water.

4. The solution of additional initiator consisted of 0.27g ammonium persulphate in 2.16g water.

5. The solution of formaldehyde derivative consisted of 0.18g of sodium sulphoxylate formaldehyde in 2.07g water.

The particle size of the dispersion was 220 nm.

The autoxidisable macromolecules could act as associative thickeners when

in a solution of pH above 7 and preferably between 9 to 9.5.

EXAMPLE 5A

Alternative Autoxidisable Cellulose-free Associative Thickener containing

Styrene as Autoxidation Promoter which will be called "Thickener Eg 5A"

The process of Example 5 was repeated except that the copolymerisable monomer

of Example 1 was replaced with the copolymerisable monomer of Example 2.

The autoxidisable macromolecules could act as associative thickeners when in a

solution of pH above 7 and preferably between 9 to 9.5.

EXAMPLE 6

Alternative Cellulose-free Associative Thickener having increased

Hydrophilicity which will be called "Thickener Eg 6": The process of Example 4 was repeated but with the following

modification:

The mixture of co-monomers and hexanol was as follows:

Ethyl Acrylate 68.00g

Methacrylic Acid 23.50g

Copolymerisable Monomer of Example 3 lO.OOg

Hexanol 0.40g

The particles of thickener had a number average particle size of 193nm and

comprised copolymeric autoxidisable macromolecules. Hydrophobic tall oil

carboxylates (the copolymerisable monomer of Example 3) were attached to the

backbone via a polyethoxy divalent group which made the macromolecules more

water-soluble on increasing the pH to above 7. The macromolecules were able to

act as associative thickeners in solutions of pH above 7.

COMPARATIVE EXAMPLE D

Associative Cellulose-free Thickener having no autoxidisable group which

will be called "Thickener Eg D":

The process of Example 4 was repeated but with the following

modification:

The mixture of co-monomers and hexanol was as follows:

Ethyl Acrylate 203. OOg

Methacrylic Acid 101.70g Styrene 15. OOg

Stearyl methacrylate 33.90g Hexanol 1.35g

The particles of thickener had a number average particle size of 191nm.

The macromolecules were able to act as non-autoxidisable associative thickeners

in solutions of pH above 7.

EXAMPLES 7 TO 10

AND

COMPARATIVE EXAMPLES A TO D

Wet- Wipe Resistance of Dried Coats obtained from Thickened Aqueous

Paints:

In Examples 7 to 10, thickened aqueous paints were made using

autoxidisable associative thickeners as provided by this invention and

conventional ingredients all as specified in Tables 1 and 2. Similarly thickened

aqueous paints were made up in Comparative Examples A to D except that

commercially available non-autoxidative associative thickeners were used in

Comparative Examples A to C and "Thickener Eg D" was used in Comparative

Example D. Again the ingredients and amounts used are specified in Tables 1 and

2.

Each paint was made up using the following procedure. The dispersant,

biocide, coalescing solvent and antifoaming agent were all dissolved in a 50%

portion of the water. The chalk, clay and rutile were added to the solution which

was then subjected to high speed dispersion using a "Dispermat" mixer operating

at 400 rpm. Meanwhile the binder latex and any accelerator and cobalt drier

needed had been stirred into the other 50% portion of the water. The thickener and ammonia were next stirred into this other portion of water and the two

portions of water were stirred together to produce the final paint formulation.

The surface was of plasterboard previously painted with Dulux Supermatt and

aged for a week prior to being coated with the test paints. Each test paint was

applied to a surface and allowed to dry for one hour at room temperature to

produce a dried coat. The dried coats were then stored at room temperatures for

periods of 1, 2, 3 and 4 weeks and after a coat had been stored for one of these

periods, its Wet- Wipe Resistance was assessed using the procedure described

earlier in this specification.

The assessments and the periods after which they are made are shown in

Table 3 together with the PVC of the dried coats and the amount (in parts by

weight) of thickener used in the aqueous paint (i.e. before the paint has begun to

dry).

Table 3 shows that the use of autoxidisable thickeners substantially

increases the Wet- Wipe Resistance of the dried coats even when the PVC of the

dried coats exceeds 70% and even when the amount of thickener used exceeds

that used for conventional non-autoxidisable associative thickeners by a factor of

at least 3 and sometimes over 5. This ability to use much larger amounts of

thickener enables thicker aqueous coating compositions to be made when the

thickener is autoxidisable as is illustrated by the viscosities shown in Table 4.

Table 3 Examples 7 and 8 demonstrate the benefits of incorporating styrene in the

macromoleclar thickener. A preliminary pre-storage inspection indicated that the autoxidation of the paint of Example 10 was slow owing to the absence of the

unsaturated accelerator.

TABLE 1

INGREDIENTS OF THE PAINT FORMULATIONS

Viscosities at increasing and decreasing shear rates were measured using a

Cari-Med CSL 100 rheometer. Measurements were made with increasing shear

rate (up) and then after a 2 minute pause, with decreasing shear rate (down). The

differences in the viscosities measured at increasing and decreasing shear rate

viscosities indicate thixotropy. All were thixotropic. TABLE 2

DETAILS OF THE INGREDIENTS

An unexpected benefit is that increased amounts of autoxidisable thickener

produced increased Wet- Wipe Resistances whereas an increase in conventional

thickener would decrease Wet- Wipe Resistance. It is presumed that this benefit is

possible because the increase in autoxidisability brings an increase in Wet- Wipe

Resistance which offsets the decrease which might be expected from an increased

amount of hydrophilic moieties. TABLE 3

ASSESSMENT OF WET- WIPE RESISTANCE ON A SCALE OF l(POOR) TO 10 (GOOD)

* Numbers in brackets refer to weight of dry thickener per 100 g of wet paint

composition

TABLE 4 VISCOSITIES OF THICKENED PAINTS

*Up **Down

Low shear = 0.1 / sec : medium shear = 40 / sec : high shear = 1000 /sec EXAMPLES 11 TO 13

Alternative Method for Providing Cellulose-free Autoxidisable thickener using Esterification and Transesterification:

Firstly, a mixture of autoxidisable hydroxy esters was made by the

alcoholysis of soya bean oil (Example 11), safflower seed oil (Example 12) or

linseed oil (Example 13). The alcoholysis was carried out using 1,3-butene diol.

To make the esters, 300.0g of one of the oils were charged under nitrogen to

a round bottom flask fitted with a reflux condenser. 1.5g of lithium neodecanoate

were added and the flask and contents were heated to 200°C for 1 hour. 61.5 g of

1,3-butene diol were added over 5 minutes followed by heating to 240° for 45

minutes. A mixture of autoxidisable unsaturated hydroxy esters was obtained.

300. Og of the mixture of esters obtained above were added to 174.0g of

methacrylic anhydride contained in a round bottom flask fitted with a reflux

condenser. O. lg of the methyl ether of hydroquinone (MEHQ) were added as a

polymerisation inhibitor and the mixture was heated to 100°C for 3 hours. An

autoxidisable monomer mixture was obtained which comprised methacrylate

moieties and unsaturated long chain moieties derived from the oil.

The autoxidisable monomer mixture was converted into an autoxidisable

associative thickener as follows. A mixture containing the autoxidisable monomer

mixture and the following was made up: Autoxidisable monomer mixture from above 30.0g

Methacrylic acid 44.0g

Ethyl Acrylate 76.0g

Sodium C₁₄ to C₁₈ sulphonate 3.0g

Water 200.0g

The mixture was emulsified by subjecting it for 5 minutes to intense agitation

provided by a Ross ME- 100 Emulsifier operating at 10,000rpm. 30.0g of the

emulsion obtained were added to 288.0g of water which had been previously

heated to 80°C under nitrogen. The reactants and water were then maintained at

80°C until the final cooling. 0.8g of ammonium persulphate in 16.0g of water

were added to the emulsion in the prior heated water and whole was allowed to

stand for 30 minutes. The remainder of the emulsion was added gradually over 2

hours and the whole again allowed to stand for 30 minutes. 0.2g of t-butyl

hydroperoxide was added followed by another 30 minutes stand. Then 0.14g

sodium formaldehyde sulphoxylate in 2.0g water was added followed by a 30

minute stand. The last two additions and stands were repeated and then the whole

was allowed to cool to ambient temperature. An autoxidisable thickener was

obtained which could be used to thicken and bind paint.

EXAMPLE 14

Use of Transesterification:

The following mixture was made: Autoxidisable monomer of Example 13 160.0g

Ethyl Acrylate 160.0g

DER 333 ( liquid epoxy resin from Dow) 3.0g

Dibutylamine 1.5g MEHQ inhibitor O.lg

The mixture was charged to a round bottom flask fitted with a glass packed

column and heated to 125°C over a period of 2.5 hours whilst ensuring that the

head temperature of the column was kept below 80°C. This caused

transesterification to occur after which a distillate of 20ml was collected from the

flask which comprised the autoxidisable monomer.

The autoxidisable monomer was used to make an autoxidisable thickener

according to the procedure of Examples 1 1 to 13 but with the following changes:

1. 7.5 g of the autoxidisable monomer were used,

2. 7.5g of methacrylic acid were used and

3. 40.0g of ethyl acrylate were used.

This thickener can be used in paint formulations as described earlier.

This invention is further illustrated by the drawings of which

Figure 1 shows a reaction scheme for introducing pendant hydrophobic moieties onto a polymeric backbone.

Figure 2 shows a polymeric backbone containing only carbon atoms.

Figure 3 shows a polymeric backbone containing both carbon and oxygen atoms.

Figure 4 shows a polymeric backbone containing carbon, oxygen and nitrogen atoms. Figure 1 shows a reaction scheme for the copolymerisation of a tall oil

methacrylate containing tall oil moiety with other ethylenically unsaturated co-

monomers to form a backbone carrying pendant autoxidisable hydrophobic tall oil

moieties.

Figure 2 shows an all carbon backbone containing 6+2n carbon atoms as

might be obtained from the free radical initiated polymerisation and subsequent

hydrolysis of vinyl acetate to give a notional polyvinyl alcohol. The chain

terminating groups are arbitrarily shown as hydrogen atoms. Pendant

hydrophobic moieties could be attached to the backbone by condensation with

hydroxyl groups.

Figure 3 shows a carbon and oxygen backbone containing 6+2n carbon

atoms and 2+n oxygen atoms. Again hydroxyl groups could be used for the

attachment of hydrophobic groups.

Figure 4 shows a backbone comprising carbon, oxygen and nitrogen atoms

as is found in ethoxy late urethanes.

Claims

1. A thickened aqueous coating composition of a chosen pH which contains a

polymeric binder and a macromolecular thickener

a) which thickener contains macromolecules having moieties which are

hydrophilic at the chosen pH and

b) which thickener on dispersion in water at a concentration of 2wt%

(based on the combined weights of the thickener and water) has a low

shear viscosity of at least 0.1 Pa.sec when measured at 18°C on a

Brookfield viscometer using a No. 3 Spindle rotating at 12rpm

wherein the macromolecules are cellulose- free and also contain autoxidisable

moieties thereby creating a cellulose-free autoxidisable thickener.

2. A composition according to Claim 1 wherein the composition contains a

drier which catalyses autoxidation of the autoxidisable moieties.

3. A composition according to Claim 1 or Claim 2 wherein the autoxidisable

moieties are provided by long chain unsaturated fatty acids.

4. A composition according to any one of Claims 1 to 3 wherein the

autoxidisable moieties are provided by a copolymerised diester comprising

a divalent hydroxypropylene group.

5. A composition according to any one of Claims 1 to 3 wherein the

autoxidisable moieties are provided by a copolymerised diester comprising

a poly ether divalent radical.

6. A composition according to any of Claims 1 to 5 wherein the

macromolecules contain copolymerised styrene or an analogue of styrene.

7. A composition according to any one of Claims 1 to 6 wherein the

composition contains a polyunsaturated compound.

8. A composition according to Claim 7 wherein the polyunsaturated

compound contains polybutadiene moieties.

9. A composition according to any one of the preceding Claims wherein the

composition contains more than 3wt% (based on the total weight of the

composition) of the thickener.

10. A composition according to any one of claims 1 to 8 wherein the

composition contains up to 3wt% (based on the total weight of the

composition) of the thickener.

11. A composition according to any one of Claims 1 to 10 wherein the

composition contains less than 30% by volume of solid material.

12. A process for making a coating composition as claimed in any one of

Claims 1 to 11 wherein the thickener is made by subjecting the co-monomers

from which the polymeric backbone is obtained to intensive agitation.

13. An architectural paint, lacquer, varnish, woodstain or adhesive comprising

a coating composition as claimed in any one of Claims 1 to 11 or made according

to Claim 12 and containing over 3wt% of the thickener.

14. An aqueous thickener dispersion of chosen pH for use in coating

compositions

a) which thickener contains macromolecules having moieties which are

hydrophilic at the chosen pH and

b) which thickener on dispersion in water at a concentration of 2wt%

(based on the combined weights of the thickener and water) has a low shear

viscosity of at least 0.1 Pa.sec when measured at 18°C on a Brookfield

viscometer using a No. 3 Spindle rotating at 12rpm

wherein the macromolecules are cellulose-free and also contain autoxidisable

moieties thereby creating a cellulose-free autoxidisable thickener.

15. A dispersion according to claim 14 wherein in the unneutralised state the

particles have a number average particle size below 500 nm.

16. A composition according to any one of claims 1 to 11 or 13 wherein the

polymeric binder and the cellulose-free macromolecular thickener comprise the

same material.

17. A composition according to any one of claims 1 to 11 or 13 wherein the dried

coat obtained from said composition has a PVC of at least 70%.